I would bet there is one mix created in surround sound (7.1 or Dolby Atmos or whatever), and then the end-user hardware does the down-mixing part, i.e. from Atmos with ~20 speakers to a pair of airpods.
In the music world, we usually make stereo mixes. Even though the software that I use has a button to downmix the stereo output to mono, I only print stereo files.
It's defintely good practice to listen to the mix in mono for technical reasons and also because you just never know who's going to be listening on what device---the ultimate goal being to make it sound as good as possible in as many listening environments as possible. Ironically, switching the output to mono is a great way to check for balance between instruments (including the vocals) in a stereo mix.
At any rate, I think the problem of dynamics control---and for that matter, equalization---for fine-tuning the listening experience at home is going to vary wildly from place to place and setup to setup. Therefore the hypothetical regulations should help consumers help themselves by requiring compression and eq controls on consumer devices!
Side tip: if your tv or home theater box has an equalizer, try cutting around 200-250hz and bring the overall volume up a tad to reduce the muddiness of vocals/dialogue. You could also try boosting around 2khz, but as a sound engineer primarily dealing with live performances, I tend to cut more often than I boost.
What the hell!
Not necessarily. Regardless of vocal range, around 400hz-2000hz makes up the body of what you hear in human speech, or the notes for instryments carrying a melody. Below that, say, 160-315hz is going to be the "warmth" and "fullness" of the sound, while 2.5khz-8khz is going to be the enunciation and clarity (think ch-sounds, ess-es, tee-s, etc).
Sure, if you start really going hard on an EQ, you could absolutely throw everything out of balance
if you cut out 12db at 250hz, all the warmth will be gone and everything will sound thin. If you scoop a bunch of 400hz-1.6khz, it will sound like a walkie-talkie, and if you make a large boost around 3khz-8khz, then everything will probably sound harsh and scratchy.
This is where, the listening environment becomes important to consider. Do you live near a busy highway or do you have a loud air conditioner? You don't need to answer these questions in public, but those kinds of ambient sounds can compete with the enunciation frequencies, or add to the buildup of "mud" in the lower part of the spectrum.
The size, shape, material properties etc. of your room and furniture also play a role here. For example, a bunch of bare walls and hard surfaces will cause a lot of the high frequencies to bounce around, potentially causing a buildup of harshness. This is why recording studios and your high school band hall probably have those oddly-shaped, cloth-covered wall "decorations" that serve to neutralize the cavernous sound you'd get in a large, bare room.
Overall, compensating for the environment is where you should probably aim your EQ. That is, even if source material varies wildly, it's probably best to try to EQ to the room you're in rather than each, individual program.
The way to do it is to find a song you know by heart, that you know how it sounds in the best way possible (there are a few that, to me, sound great in my car and on my favorite pair of headphones, so I use those), and play that through your TV. Then, fiddle with the EQ until it's as close to the ideal sound in your head as you can get it.